As is known, the seals with which lubricants come into contact during use can be made from any of a variety of materials (generally an elastomer such as a nitrile rubber, an acrylic rubber, a silicone elastomer, or a fluoroelastomer) which can shrink in contact with some lubricants, such as poly-.alpha.-olefins. Shrinkage of the seal, of course, can eventually result in leakage, so it is recognized to be desirable to incorporate seal-swell agents into lubricants in order to counteract the seal shrinkage that could be caused by the lubricant in the absence of the seal-swell agent.
The materials normally recommended for use as seal-swell agents are esters, which are ordinarily employed at concentrations of .about.5%, based on the total weight of the lubricant composition. Of these esters, some are too volatile to be utilized in lubricant formulations that will be exposed to very high temperatures. Others, such as ditridecyl adipate, have practical utility and can provide adequate swelling of some seals when employed at the recommended 5% concentration. However, it would be desirable to find seal-swell agents that would be effective in swelling more seal materials and could be used in smaller concentrations since:
(1) the other additives commonly employed in lubricant compositions (e.g., viscosity improvers, pour point depressants, extreme pressure agents, antioxidants, and antiwear agents) have to be in balance to work effectively, PA1 (2) the inclusion of another additive, such as a seal-swell agent, upsets this balance, thus decreasing the effectiveness of each of these common additives, and PA1 (3) the degree to which the effectiveness of these additives is decreased by the inclusion of an additional additive, such as a seal-swell agent, appears to increase as the amount of the additional additive is increased.